A silent chain is generally formed of link plates, each having a pair of pin insertion holes and a pair of sprocket-engaging teeth, the link plates being disposed in rows extending widthwise of the chain, and the link plates of each row being displaced in the longitudinal direction of the chain relative to, and interleaved with, the link plates of an adjacent row, the interleaved link plates being arranged to form an endless loop. The chain has guide plates, each having a pair of pin holes, disposed on both sides of the chain. Connecting pins, secured to pin holes of the guide plates, extend through pin holes of the link plates. The connecting pins are typically rocker pins composed of a long pin and a short pin, or single pins having a circular cross-section.
When the silent chain travels between a driving sprocket and a driven sprocket, the adjacent rows of link plates can rotate relative to one another about the connecting pins. Polygonal motion of the chain as it engages and disengages a sprocket, causes vibration in the free spans of the chain between the sprockets, and the relative rotation of the link plates about the connecting pins allows the free span of the chain to flex freely, causing the generation of noise.
To suppress vibration noise, spring links or plate-shaped springs have been provided at a central location widthwise of the chain to bias the link plates of the chain laterally outward toward the guide plates. The biasing force exerted by the spring links or plate-shaped springs increases the surface pressure exerted between adjacent link plates, restricting relative rotation of the adjacent link plates and thereby suppressing noise due to vibration in the free span regions of the chain. This approach is described in Japanese Laid-Open Patent Publication No. Hei-8-74939 and Japanese Laid-Open Patent Publication No. 2000-304105
A conventional rocker pin type silent chain 21 is shown in FIGS. 9 and 10 of this application. Widthwise rows of identically shaped link plates 24, each having a pair of pin holes 22 and a pair of teeth 23, are displaced longitudinally relative to one another, and interleaved and pivotally connected by connecting pins 27, which extend through the pin holes 22 of the link plates. Each connecting pin 27 is a rocker pin comprising a long pin 25 and a short pin 26. The ends of the long pin 26 are secured to non-circular pin holes 29 in guide plates 28 disposed on both outer sides in the direction of the width of the chain. The long pin 25 and the short pin 26 have substantially the same cross-sectional shape, and the back surfaces of the long and short pins roll against each other, allowing the adjacent rows of link plates 24 to rotate relative to one another.
Spring links 30 are provided centrally in the direction of the width of the silent chain 21. These spring links exert a biasing force pressing the link plates 24 toward guide plates so that the pressure at the contacting surfaces of the adjacent link plates is increased. As a result, relative rotation of the adjacent link plates 24 is restricted, and noise due to vibration in the free span region of the chain is suppressed.
While the centrally located spring links 30, as shown in FIGS. 10 and 11 are effective in reducing noise, the operation of the chain can result in uneven sprocket wear. The portions of the sprocket teeth 31 that are engaged by the link plates 24 wear as a result of repeated contact, but the link plates do not cause wear at the location of the gap between the left and right groups of link teeth, where the spring links 30 are located. Thus, as shown exaggeratedly in FIG. 11, a step 32 is generated on the sprocket tooth surface. If the silent chain 21 is shifted, for example as a result of vibration, the chain can run on the step 32 and generate noise, and the chain can even disengage from the sprocket. Furthermore, since the spring links 30 are additional parts, the width and weight of the chain are increased, and the parts count and cost of manufacture are increased. These problems exist not only in the rocker pin type silent chain, but also in a round pin type silent chain in which spring links are provided.
Accordingly, objects of this invention include the solution to the above-mentioned problems, and the provision of a silent chain which can suppress noise due to vibration in its free span regions, and at the same time prevent the generation of steps due to wear of the sprocket teeth and avoid an increase in the number of parts of the chain and an increase of the chain width.